This application is a continuation-in-part of Copending Application Ser. No. 766,542 filed Aug. 19, 1985 now abandoned.
The aircraft pitch control system of the present invention is of the same general type as the "Flying Tail" described in Richter U. S. Patent 3,949,958. The Richter system involves a movable tail comprising a stabilizer actuated by a number of hydraulic actuators, and manually controlled hydraulically operated elevators. The resulting movable tail surfaces provide moments about the center of gravity of the aircraft when the stabilizer and/or elevators are inclined to the air flow.
The Richter "Flying Tail" is designed for large air-craft, and it includes four independent hydraulic systems for operating the stabilizer. These multiple hydraulic are provided for redundancy purposes, because the absence of hydraulic power eliminates all horizontal tail control in the Richter system.
The pitch control system of the present invention, on the other hand, includes an emergency lock for the stabilizer, which operates in the event of power failure, so that pitch control of the aircraft may be carried out manually in the event of such failure. The system of the invention is particularly intended for small aircraft, and because of its ability to exert a manual control in the event of power failure, obviates the need for redundant hydraulic controls for the stabilizer.
It is accordingly an objective of the present invention to provide an improved pitch control system of the type described above, and which is constructed to enable the pilot to revert to manual control in the event of failure of the stabilizer actuator.
A feature of the invention is that because of the ability of manual control of the system in the event of actuator power failure, the stabilizer in the pitch control system of the invention may be actuated by standard hydraulic, pneumatic or electrical power systems, as opposed to the powered stabilizer described in the Richter patent which requires a plurality of independent redundant hydraulic systems to control the stabilizer section of the tail, because absence of hydraulic power eliminates all horizontal tail control in such systems.
The pitch control system of the invention may be constructed to vary its control effectiveness by changing the relationship between the motions of the stabilizer and elevators as a function of flight speeds. At low speeds, large stabilizer movements provide more tail control in a situation where aerodynamic forces are low; whereas at high speeds, it is desirable to provide a lesser stabilizer motion relative to elevator motion because the aircraft is then sensitive to small stabilizer movements when the aerodynamic forces are large.
The foregoing requirement is implemented by an electronic control unit which adjusts the servo response to elevator motion as a function of indicated air speed. By such a control, the desired aircraft acceleration as a function of pilot pressure on the pitch control may be achieved over a wide speed range.